Low-concentration phytotoxic micronutrient compounds for selective control of invasive plant species

ABSTRACT

This invention provides low-dose, low-concentration formulations of phytotoxic trace inorganic compounds for use in methods and systems for selectively and effectively controlling invasive plants.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.61/784,778 filed on Mar. 14, 2013, U.S. provisional application No.61/752,605 filed on Jan. 15, 2013, and U.S. provisional application No.61/752,681 Filed on Jan. 15, 2013, each of which is hereby incorporatedby reference in its entirely for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISC APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to compositions, processes and systems for thecontrol and eradication of invasive plant species (i.e. weeds)(dandelion, spotted knapweed, cheatgrass and others).

2. Basis for Invention

Invasive weeds are a serious world-wide problem and about 5% of theworld economy (˜$1.4 T) is spent annually on control. The approach toweed control currently used is ineffective, expensive and causesexcessive harm to the environment. The current global practice for weedcontrol involves spraying chemical weed control formulations on thelive, above ground tissue of growing plants to selectively disrupt thephysiological processes of the plant.

Invasive species are adapted to nutrient-poor soils and out-competedesirable native vegetation once established. As the human populationhas swelled from 1 B to more than 7 B people over the past 200 years nocorner of the globe has been spared from land disturbing activitiesincluding grazing, mining, logging, road building, urbanization, andcrop production. In many cases land disturbances are severe and nativesoils have become depleted of nutrients (i.e. disturbed) resulting in anet ecological shift away from soils in geochemical equilibrium with theoccupying plant community toward invasive species dominated soils withlow fertility.

Plant-soil equilibrium exists through recycling of soil nutrients bydecay of above ground biomass. Disequilibrium occurs when the aboveground biomass is removed (e.g. heavy grazing or fire) and return ofnutrients to the soil greatly reduced. The net condition of global soilis one of declining health and mining of soil nutrients withoutreplacement. Declining soil health, declining plant production andinvasion by weeds are the result. Agrarian societies dependent onagriculture output are diminished and made less secure.

In order to address this long-felt need for weed control on disturbedlands, the present invention provides environmentally-friendly,cost-effective compositions, methods and systems for the control ofunwanted plants on disturbed soils.

SUMMARY OF THE INVENTION

The present invention provides low-dose, low-concentration formulationsof phytotoxic trace inorganic compounds for use in methods and systemsto selectively and effectively control invasive plants. According tosome embodiments of the present invention, the formulations can beapplied as dry products or as a liquid.

According to the present invention, the formulations of the presentinvention are applicable to selectively and effectively control thegermination of invasive plant seed and cause death to emerging invasiveplant seedlings and mature plants. Accordingly, advantages compared toconventional methods for control of invasive plants include destructionof seed reserves stored in soil, selectiveness of phytotoxic effectspecific to invasive plants, exceptionally low cost per unit area ofcontrol, and selective persistence of desirable target species. Traceelements are water-soluble, soil adsorbed, and non-carcinogeniccompounds having no known endocrine disruption properties. The presentinvention takes advantage of the fact that trace inorganic compounds arenaturally occurring and required for plant growth as micronutrients.According to the present invention, replacement of adequate quantitiesof trace elements restores soil health to support desirable plantspecies and results in the control or eradication of undesirableinvasive plants.

The present invention provides methods and systems for controlling thegrowth of invasive plant species comprising the steps of applying anaqueous solution of at least one micronutrient having a concentration ofthe micronutrient of from about 0.5 milligrams per liter to about 50milligrams per liter to a locus to be treated with an application of2-200 milliliters per square meter.

In some embodiments, the methods and systems of the present inventionuse aqueous solutions comprising at least one micronutrient selectedfrom the group consisting of boron, copper, manganese, molybdenum,chloride, zinc compounds, and combinations thereof.

In some embodiments, the methods and systems of the present inventionuse aqueous solutions which also include liquid water.

In some embodiments of the present invention, the locus to be treated isselected from the group consisting of disturbed land, urban land,rangeland, forestland, roadside, brownfield and cultivated land.

In some embodiments of the present invention, the locus to be treatedcomprises invasive plant species selected from the group consisting oflive plants on the soil surface, seed, senesced seed-bearing plants, andlive seed-bearing plants.

The present invention also provides methods and systems of controllingthe growth of invasive plant species comprising the steps of applyingfrom about 0.5 to about 20 pounds of at least one water solublemicronutrient per acre as a dry product to a locus to be treated.

In some embodiments of the present invention, the at least one watersoluble micronutrient is selected from the group consisting of boron,copper, manganese, molybdenum, chloride or zinc compounds, orcombinations thereof.

In some embodiments, the methods and systems of the present inventionfor controlling the growth of at least one invasive plant species at alocus to be treated involve determining an invasive plant species to becontrolled at the locus to be treated; measuring the solublemicronutrient concentrations in soil at the locus to be treated;determining at least one micronutrient to be applied to control theinvasive plant species; and applying the at least one micronutrient tothe locus to be treated to achieve a growth controlling effectivesoluble concentration of the at least one micronutrient in the soil atthe locus to be treated.

In some embodiments, the methods and systems of the present inventionare used to prevent growth of invasive plant species by applying atleast one micronutrient to an area to be treated to achieve a solublemicronutrient concentration in soil of the area to be treated of fromabout 0.5 milligrams to about 50 milligrams per liter.

In some embodiments, the methods and systems of the present inventionprevent plant growth on an area to be treated by applying a toxic amountof at least one micronutrient to the area to be treated.

All patents, patent applications, provisional patent applications andpublications referred to or cited herein, are incorporated by referencein their entirety to the extent they are not inconsistent with theteachings of the specification.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A illustrates the percent mean plant cover of dandelion (Taraxacumofficinale), cheatgrass (Bromus tectorum) and perennial grass (severalspecies) over a 5 year time period following application of dryformulations of varying boron concentrations at a field site inBelgrade, Mont.

FIG. 1B illustrates the percent mean plant cover of dandelion (Taraxacumofficinale), cheatgrass (Bromus tectorum) and perennial grass (severalspecies) over a 5 year time period following application of liquidformulations of varying boron concentrations at a field site inBelgrade, Mont.

FIG. 2A illustrates one hundred percent (100%) cheatgrass seedgermination five days post wetting with distilled water (controltreatment).

FIG. 2B illustrates zero percent (0%) cheatgrass seed germination 14days post treatment with boron solution at an effective concentration of10 mg/L.

FIG. 3A illustrates the growth of invasive species dandelion (Taraxacumofficinale) in a small pot study with varying soil boron concentrationsof 5, 10, 25 and 50 mg/L compared to plant growth in pots watered withtap water and a commercial fertilizer.

FIG. 3B illustrates the growth of invasive species spotted knapweed(Centaurea maculosa) in a small pot study with varying soil boronconcentrations of 5, 10, 25 and 50 mg/L compared to plant growth in potswatered with tap water and a commercial fertilizer.

FIG. 3C illustrates the growth of desirable species bluebunch wheatgrass(Pseudoroegenaria spicata) in a small pot study with varying soil boronconcentrations of 5, 10, 25 and 50 mg/L compared to plant growth in potswatered with tap water and a commercial fertilizer.

FIG. 3D illustrates the growth of both desirable species bluebunchwheatgrass (Pseudoroegenaria spicata), Kentucky bluegrass (Poapratensis) and invasive species dandelion (Taraxacum officinale),spotted knapweed (Centaurea maculosa) and cheatgrass (Bromus tectorum)in a small pot study with a fixed soil boron concentrations of 10 mg/L.

FIG. 4 illustrates rangeland site cheatgrass percent plant cover over afive-year study period in response to water soluble boron concentrationsin soil caused by surface boron applications resulting in soil boronconcentrations greater than 20 mg/L.

FIG. 5A illustrates rangeland site cheatgrass (Bromus tectorum) percentplant cover over a two-year study period in response to water solubleboron concentrations in soil resulting from liquid surface boronapplication.

FIG. 5B illustrates rangeland site cheatgrass (Bromus tectorum) percentplant cover over a five-year study period compared to perennial grasscover in treated (10.3 mg B/L) and untreated (2.9 mg B/L) areas.

FIG. 6 illustrates the results of a greenhouse study of live cheatgrass(Bromus tectorum), dandelion (Taraxacum officinale), spotted knapweed(Centaurea maculosa), Kentucky bluegrass (Poa pratensis) and bluebunchwheatgrass (Pseudoroegneria spicata) plants in response to solutions ofincreasing boron concentration, as reflected in plant health index.

FIG. 7 illustrates live, near-mature cheatgrass plant responses, asmeasured by plant health index, to short-term application of variousboron solutions. Solutions contain increasing concentrations of boronmixed with deionized water, compared to tap water.

FIG. 8 illustrates percent germination of cheatgrass, dandelion, spottedknapweed and Kentucky bluegrass seed in a controlled benchtop(greenhouse) experiment ten (10) days post treatment of seed withsolutions of increasing boron concentration.

FIG. 9. Illustrates an idealized invasive species and desirable plantspecies wherein the invasive species is less tolerant of increasing soilmicro-nutrient compounds compared to the desirable plant species. TheInduced Phytotoxicity Threshold (IPT) shown constitutes the target levelfor micro-nutrient addition to the soil to cause phytotoxic control ofthe invasive plant species while causing no harm to the desirable plantspecies.

DETAILED DESCRIPTION OF INVENTION

Invasive plants (i.e. weeds) are well established across the globe andcontribute to economic losses, habitat degradation, losses in landproductivity and value. Weeds have become established through a varietyof landscape changes including, but not limited to, fire, grazing, landclearing, tillage, urbanization, and other land disturbing activities.Weed seeds have also traveled the globe becoming established as exoticspecies on continents on opposite sides of the world. Many of thenoxious weeds found in the U.S. evolved naturally elsewhere and becomeestablished and proliferate in the absence of natural controls.

Billions of dollars are spent annually controlling weeds. The NatureConservancy Global Invasive Species Team reports world-wide damage frominvasive species amounts to $1.4 trillion annually, or five percent ofthe global economy (Pimentel et al. 2001). In the U.S. impacts frominvasive amount to $120 billion annually with more than 100 millionacres affected (Pimental et al. 2005). Leafy spurge (Euphorbia esula)infestations in the northern Great Plains costs ranchers $120 millionannually (Bangsund et al. 1991).

Herbicides are the principal strategy for controlling weeds includingSynthetic formulations such as glyphosate (ROUNDUP®/Monsanto, andothers), PLATEAU® (imazapic, BASF), JOURNEY® (imazapic+glyphosate,BASF), MATRIX® (sulfonylurea, DuPont), LANDMARK XP® (sulfometuron andchlorsulfuron, Dupont), OUST® (sulfometuron, DuPont) and otherformulations are sold to control weeds. Effectiveness of conventionalherbicide applications is highly dependent on timing of herbicideapplication relative to both plant physiology/growth stage, specificcontact with growing vegetation, and complimenting rainfall conditions.The cost of chemical control can be as high as $250 per acre or greaterwith repeated applications. Land managers often rule out the use ofherbicides for control of weeds due to high cost, low effectiveness anddamage to desirable species. Effective weed control methods which do notharm desirable species are available, but often have limitations relatedto cost, need for repeated application and a general concern for thehazards associated with the application of organic chemicals in theenvironment. Most herbicides used for control of invasive species areorganic liquid chemicals applied to the leaf tissue which result indisruption of plant metabolic processes. These same organic chemicalsare not naturally-derived and may be harmful to water quality, wildlifeand humans. Additionally, research suggests that some invasive plantspecies are developing resistance to herbicides (Maxwell et al. 1990;Heap 2006) and the herbicide in most widespread use across the world(i.e. glyphosate) may cause unintended consequences including limitingmicronutrient availability (Yamada et al. 2009), as well as broadendocrine disruption.

Of the sixteen chemical elements known to be important to a plant'sgrowth and survival, thirteen come from the soil, are dissolved in waterand absorbed through a plant's root system. In some instances, there areinsufficient levels of these elements to sustain normal plant growth anddevelopment. Agriculturalists rely on the application of fertilizer toameliorate elemental nutritional deficiencies, with the expectation of apositive, ‘desirable’ plant response to the added nutrient. It is knownthat all plant species have definable nutrient requirements and manyplant species have unique sensitivities to trace elements, otherwiseknown as micro-nutrients. Some combinations and concentrations of thesenutrients, particularly the micronutrients, can be detrimental or toxicto some plants. Sensitivities to low or high micro-nutrient levels canbe expressed in plants as depressed or stunted growth, delayed maturity,incomplete physiological development, cell necrosis, or premature death(Kabata-Pendias and Pendias, 2001). The range of micronutrients requiredfor optimal plant growth for each species may be broad or narrow. Soilshave unique geochemical characteristics related to climate and parentmaterial. Native plant communities have adapted to these uniqueconditions over thousands of years. Under natural conditions theseplant-soil systems maintain an equilibrium level of nutrientavailability until disturbed by natural or anthropogenic forces causinga geochemical disequilibrium which makes these plant-soil systemssusceptible to invasive species colonization.

Phytotoxic levels of trace elements in soils are known to occurnaturally. Acid-sulfate soil systems are known to mobilize metalsresulting in phytotoxic soil conditions for plant species not tolerantof soil acidity. Saline soil conditions are also known to occur in aridclimates resulting in phytotoxic conditions for plant species nottolerant of elevated salinity. Anthropogenic releases of contaminants tothe natural environment are also known to cause phytotoxic soilconditions. Mining and smelting are both known to cause acidic andmetalliferous soil conditions, while agricultural practices such asfallow farming may lead to salinization of the soil resource.

Farmers may add fertilizers or soil amendments to increase the yield ofcrops and overcome any geochemical limitations of the soil which affectscrop yield. The plant macronutrients nitrogen, phosphorous and potassiumare routinely added to soil to maximize yield. In some cases traceelements such as copper, zinc or boron may be added to the soil if thecrop grown has unique trace element fertilization needs for maximumyield. Farmers may also add soil amendments such as lime (CaCO₃) tocontrol soil acidity. Similarly, land reclamation scientists may addsoil amendments and fertilizers to control undesirable soil geochemistryat disturbed sites. Seeding of plant species which are tolerant ofsite-specific conditions is also a common practice for revegetation ofdisturbed sites.

According to the present invention, minute concentrations of the plantmicro-nutrients boron, copper, zinc, manganese, chlorine and molybdenumwhen applied to the soil, directly to weed seed, or to soil containingweed seed, result in seed death, failure of weed seed to germinate, andpre-mature mortality of emerging seedlings through micro-nutrientinduced phytotoxicity. According to the present invention, soilconditions phytotoxic to weed species yet not phytotoxic to desirableplant species are made possible through knowledge of the dose-responsecurve for each unique micronutrient-plant interaction. The resultingmodified geochemical soil conditions cause selective phytotoxic controlof invasive plant species while allowing establishment and persistenceof desirable plant species. Timing of application of the micro-nutrientis targeted to elevate soluble soil micronutrient concentrations in soilcontaining weed seed prior to seed germination. Thus, micro-nutrientapplication can be made any time following weed seed drop and beforeweed seed germination. The timing of micronutrient application is uniqueto the invasive species targeted and its growth cycle. Fundamentally,the elevated soil micronutrient conditions must exist while the plant isactively growing (whether seed is germinating below the soil surface orproducing leaf tissue above the soil surface). The period ofmicronutrient application may encompass the entire calendar year,depending on the plant species and site conditions including compositionof desirable plant species present.

According to the present invention, mature growing invasive species canbe controlled by micronutrient addition. For example, weeds commonlygrow to maturity early in the growing season and may produce and dropseed in late-spring to mid-summer. Selective control of invasive plantspecies by applied inorganic micro-nutrient-induced phytotoxicity hasnot been previously reported in the scientific literature. Organicchemical herbicides for control of invasive species are known.Phytotoxicity to plants due to micronutrient imbalances are known.However, prior to the present invention, the selective control ofinvasive species described herein by micro-nutrient inducedphytotoxicity in the soil has not been previously reduced to practice.

According to one exemplary embodiment the present invention, themicronutrient boron is used to illustrate the plant response of tworepresentative desirable plant species (bluebunch wheatgrass andKentucky bluegrass) and three representative invasive plant species(cheatgrass, dandelion and spotted knapweed). As used herein, thephrases “desirable plant species” and “desirable plants” refer to plantsthat are present in a specific location where they are wanted. As usedherein, the phrases “invasive plant species” and “invasive plants” referto plants that are present in a specific location where they areunwanted. Thus, according to the present invention, whether a plant isconsidered a desirable or an invasive plant in a particular situationdepends on the specific location involved and the desires of the manageror owner of that location. For example, a certain grass species may beconsidered a desirable plant in a mixed alfalfa/grass field used forforage production or livestock grazing. That same grass species,however, may be considered an invasive plant in an alfalfa field to beused for certified alfalfa seed production. In the latter situation, thegrass species would be classified a weed and if too many seeds or otherparts of the grass species were harvested with the alfalfa seed that mayresult in the seed from that alfalfa production field being deniedcertification. On an un-tilled landscape occupied by native vegetationthe colonization of the site by non-native or exotic plants isillustrative in that the native vegetation would be the “desirablespecies” and the non-native and exotic colonizing species would be an“invasive species”.

According to other embodiments of the present invention, the control ofinvasive plant species shown herein by using various boron solutions isalso applicable and demonstrated using other micronutrients and otherspecies and combinations of species. This disclosure is not intended tobe limited to the invasive species provided as examples. A partial listof known invasive species would include, but not be limited to:cheatgrass, dandelion, knapweeds (spotted, diffuse, Russian), bindweed,chickweed, ground ivy, Canada thistle, burdock, houndstongue, yellowstar thistle, Himalayan bush clover (lespedeza), privet, Russianthistle, kochia, halogeton, Japanese knotweed, leafy spurge, St.Johnswort, toadflax (yellow and Dalmation), tansy, whitetop, hawkweed,cinquefoil, ox-eye daisy and others either known to be a problematicinvasive species and also those not yet determined to be such.

Cheatgrass, a non-native, invasive, Euro-Asian winter annual grassspecies, is present or dominant on some 100 million acres in the GreatBasin and Intermountain West. Several thousand new acres are invaded bycheatgrass every day, with each plant producing upwards of 1,000 seeds.Cheatgrass is a principal driving force behind epidemic wildfiresoccurring continually and with greater frequency across the western U.S.and is largely responsible for decline of the sagebrush-steppeecosystem, home to more than 1500 species of birds, vertebrate, andinvertebrate species including iconic western ungulates deer, elk,antelope, and the endangered sage grouse; all of which are dependent onthe habitat and health of this rapidly declining ecosystem. Thus, in oneembodiment, the present invention provides a method for soil applicationof a low-concentration liquid spray mixture of boric acid, sodiumborate, sodium tetraborate, or disodium tetraborate, or other solublesources of boron, applied to field sites to control cheatgrass and othernon-desirable annual grass species.

This invention demonstrates that fertilization by micronutrients isselectively harmful to invasive plants while desirable species areeither stimulated or tolerant of the same levels shown to be phytotoxicto the weedy species. This makes ecological sense as later successionalplant communities have more highly evolved nutrient cycling and elevatedlevels of fertility. The desirable plants characteristic of the latesuccessional plant communities are tolerant and benefit from higherlevels of soil fertility and especially adequate amounts of traceelements (also known as micronutrients). Invasive species are intolerantof elevated micronutrient levels and thrive in low nutrient soils. Therecycling of trace elements by later successional plant communities mayhave been a primary natural control on preventing weed invasion. Upondisturbance and loss of pre-disturbance fertility native plantcommunities become susceptible to weed invasion. The recovery of thesesystems through natural soil building and plant succession is likely tooccur over long periods of time (hundreds to thousands of years) absentrepeated disturbance. Consider a logging road built through a mountainmeadow. The predisturbance desirable diverse vegetation exists on bothsides of the road while the road bed and cut/fill slopes becomecolonized by invasive species. Of relevance to the invention is thatwhile the invasives produce large amounts of seed that fall on theadjacent mountain meadow they fail to become established. Trace elementphytotoxicity to such weed seeds is an important control on the invasionof weedy species such as dandelions beyond the road bed. In thisinvention soil health of disturbed lands is restored by reverseengineering the inorganic trace element/micronutrient fingerprint of thepre-disturbance soil and soil micronutrients are added resulting in thephytotoxic control of invasive plant species.

According to the present invention, any micronutrient fertilizer may beused, applied alone or in combination with other micronutrients, or evenin combination with macronutrients such as nitrogen, phosphorous, andpotassium. Central to this invention is the discovery that weeds arenegatively impacted by small quantities of micronutrients whereas moredesirable species (perennial grasses, native forbs) are tolerant ofthese same levels. The present invention demonstrates that there is adifferential tolerance between invasives and desirable plants. Forexample, consider the micronutrient copper, its total elemental amountin a given soil might be 50 mg/kg with maybe 0.1% plant available copperin any given year. If inputs and outputs of copper are in balance, thetotal amount of copper remains at 50 mg/kg and the plant availableamount remain at 0.1% of the total. In the example of overgrazing,copper translocated to the above ground biomass is removed from thesystem and micronutrient recycling to the soil is disrupted. Over timethe total amount of copper in the soil begins to decline to <50 mg/kg,but more significantly the plant available amount of copper sharplydeclines (the total elemental amount is attributable to geologicmaterials and is often very slowly weathered to plant available forms).For the sake of this example (and in parallel with observationssupporting this invention), let's say that weeds are not tolerant ofmore than 0.1% plant available copper. If that level drops due toovergrazing to say 0.01% plant available copper the site would likelybecome colonized by invasive plants if an invasive plant species seedsource is nearby. In this invention, fertilizing the soil to restore thepre-disturbance plant available copper level (target of 0.1%) wouldresult in reduction or elimination of weeds and reestablishment of moredesirable plant species either through natural recolonization orreseeding. The copper fertilizer to be used could be applied as one ofseveral compounds such as shown in Table 1. Fertilizer micronutrientformulations are highly soluble compared to geological mineral sourcesin the natural soil.

TABLE 1 Fertilizer sources of copper. Source Formula Percent CopperCopper chelate Na₂CuEDTA 13 Copper sulfate CuSO₄•5H₂O 25 Cupric oxideCuO 75 Cuprous oxide Cu₂O 89

According to the present invention, in order to calculate the rate of amicronutrient fertilizer that may be applied, following are severalcalculations based on the above table. If one wanted to add 10 pounds ofplant available copper per acre using copper chelate fertilizer youwould apply 76.9 pounds of copper chelate per acre since the fertilizeris only 13% copper. Similarly, for the same amount of plant availablecopper per acre using copper sulfate, one would apply 40 pounds offertilizer per acre as copper sulfate, or 13 pounds of cupric oxide peracre, or 11.2 pounds of cuprous oxide per acre. Any copper containingfertilizer source could be used to provide the plant available copper.Similar calculations would apply to any other micronutrient beingapplied at a target rate reflecting the percentage of the micronutrientin each unique fertilizer compound.

Whether the formulation is applied as a dry formula or as a liquidformula is irrelevant as the objective is to achieve the desired amountof fertilization in the soil to favor the species desired and reduce oreliminate the invasive weedy species. The products described in Table 1are dry and could be applied to the soil surface in the dry form with atractor/spreader. The dry fertilizer would become available to the plantupon rainfall or snowmelt. Conversely, the products could be dissolvedin water and applied with a sprayer as long as the application rates areappropriate to achieve the desired fertility goal. The products could bedissolved in any liquid not harmful to plants and applied as the liquidis only the carrier to achieve the loading rate.

In one aspect, this invention is fundamentally about massbalance—restoring appropriate amounts of soil micronutrients in soil byreplacing micronutrients lost due to land disturbance. According to thepresent invention, the consequences of restoring pre-disturbance levelsof soil micronutrients include making the soil inhospitable to invasivespecies.

In another aspect, this invention is about a hypothesis and carefulobservation of the differential sensitivities of weeds compared to moredesirable species to micronutrients.

How much micronutrient fertilizer to add is a function of the existingamount of micronutrients in the soil and the specific weedy and specificdesirable plant species present at a site on which the invention is tobe practiced. The amount of micronutrients present in a disturbed soilis a unique quantity that can be measured by laboratory analysis.Geologic parent material, soil formation history, land use history,climate and other factors influence the elemental levels of allinorganic constituents in the soil. The process to determine thespecific micronutrients and amounts of each to be applied involvescollecting samples of soil from at least two representative areas orsites: at least one sample from an undisturbed portion of the site withdesirable plant species and at least one sample from a disturbed portionof the site with invasive plant species and diminished desirable plantspecies cover. The difference in soil micronutrient levels between the“good” site and “bad” site form the basis for calculation of fertilizerapplication rates. The amount of micronutrient fertilizer added is thedifference between the degraded site with low fertility and thereference site with natural levels of soil fertility. According to thepresent invention, site specific fertilizer prescription can bedeveloped and applied. In larger landscapes with common soil andvegetation characteristics generalized micronutrient applicationstrategies may be applicable to representative areas. Also whenundisturbed sites cannot be found on the larger landscape, generalizedmicronutrient application may be required to control the targetedinvasive species.

Plant micronutrient levels in soil are generally very low (roughly a fewpounds per acre of a given plant available micronutrient).Correspondingly, the amount of micronutrient fertilizer to be added peracre would also be low and dependent on the elemental levels ofmicronutrient in the fertilizer to be applied. In the case wherefertilizer is impractical to apply at low rates (a few pounds per acre)due to the difficulty of applying a thin uniform amount of fertilizerusing mechanical equipment, the fertilizer can be bulked up to addweight and/or volume to aid in spreading. Bulking of fertilizer can beaccomplished using sand, rice hulls, corn meal, sawdust, crushed walnutshells, corn stover or equivalent. For example if the target fertilizerapplication rate was 5 pounds per acre and the reasonable minimumapplication rate with a given piece of equipment was 10 pounds per acrean additional 5 pounds of bulking material could be added to the 5pounds of fertilizer (the active ingredient).

A second factor affecting the amount of fertilizer to be added is theplant species present—both desirable and invasive. In this invention itis recognized that each plant species has a unique trace elementrequirement: too little of a given micronutrient and the plant isdeficient, too much of a given micronutrient and the plant experiencesphytotoxicity. In making this invention, I have observed that invasivespecies have lower tolerance to a given soil micronutrient concentrationcompared to desirable plant species (typically perennial grasses). See,e.g., FIG. 9. It is this differential sensitivity to micronutrients inthe soil shown by desirable plants compared to invasive plant speciesthat is fundamental to the invention. The application of this technologywill establish the levels of one or more micronutrients above phytotoxiclevels for invasive plant species and below levels harmful to desirablespecies for a given site. All data collected to date have shown thatperennial grass species are much more tolerant of elevated micronutrientlevels compared to weeds. This information is not known in thescientific literature, nor is the control of invasive species bymicronutrient fertilization practiced.

Micronutrient application to the soil can occur at any time during theyear; however maximum affect has been observed when micronutrientfertilizer is applied in the late summer/early fall or early spring inadvance of seasonal plant growth. In western landscapes occupied byinvasive weeds, winters are typically cold with snow and frozen ground.Maximum plant growth typically occurs in the spring (April-June whensnow melts, ground thaws, soil temperatures warm and spring rainsoccur). The effect of soil micronutrient application during this periodmay not be observed for one year as plant growth occurs due to existingsoil nutrients rather than the added soil nutrients (unless fertilizeris applied early in the spring and/or unless significant rainfalloccurs). Invasive plant species appear most sensitive to elevatedmicronutrient levels when the plants are young. It should be noted thatthe effect on invasive plants from micronutrient additions to soil aredissimilar from organic chemical based herbicides that kill plants overa period of days to weeks and are generally applied to the growing leaftissue. This invention requires sufficient time for the fertilizer to beapplied to the soil, become dissolved by rainfall or snowmelt and tochange the chemistry of the soil solution such that germinating seed oryoung plants imbibe the applied trace element solution. Changes to theplant community are best observed over long-periods of time(months-years) compared to conventional organic herbicide applicationsthat take affect over short periods of time. It is unclear whethermature, perennial invasive weeds can be controlled using this method.However, data shows that emergent and young invasive plants (annual orperennial) are readily controlled. This invention also should be thoughtof in terms of greatly reducing the prevalence of weeds by changing thesoil chemistry, but not eliminating all weeds. This is an ecologicalapproach to restoring desirable plant communities and their soilquality. This approach to weed control is fundamentally different thanthe current practice which focuses solely on the plant and invasivespecies control as a one component system. This invention changes thesoil chemistry to change the plant community as a two component system,each dependent on the other.

The present invention provides a method for preparation of a phytotoxicsoil condition to invasive plant species through the application ofmicronutrients. The formulations of the invention can alternatively beapplied as dry powder or as pelletized form offering residual controlspecifically targeted to seed reserves. According to the presentinvention, the specific delivery/formulation is less important thanbeing able to control the rate of application relating to theappropriate mass-balance of the micronutrient.

In some embodiments, the present invention involves using amultifunctional surfactant/dispersing agent/thickener/stabilizer whenapplying the micronutrients to reduce surface tension, improve plantsurface adhesion, soil penetration and rewetting and/or to keep allcomponents in a suspension. Alternatively, a separate surfactant/wettingagent and a thickener/stabilizer may be used to accomplish any or all ofthe above functions. In addition, a multifunctionalchelator/dispersant/stabilizer may be included to chelate any of themetal ions present such as the calcium and to trap the excess calciumfor later release.

In some embodiments, the present invention involves using a chelatingagent when applying the micronutrients. A chelate increases thesolubility of the metallic ions and favor the transportation of metallicions inside the plant. Furthermore, after binding to the metallic ionand later on depositing the metallic ion in the place where the plantrequires it, the organic part of the chelate returns to dissolve moreions, which makes the use of the micro nutrients in the soil moreprolonged.

In some embodiments, the present invention involves using a surfactantwhen applying the micronutrients. Use of a surfactant results in a highmoisturizing ability and a capacity to decrease the superficial surfacetension of the water, which facilitates assimilation of nutrients. Onthe other hand, due to the ability of the surfactant to form emulsions,the surfactant gives stability to the fertilizer.

The text below offers the example of plant micro-nutrient boron althoughthe same result can be understood by one skilled in the art to alsoapply to other plant micro-nutrients including, copper, zinc, manganese,iron, chlorine and molybdenum. The expectation is that each invasive orweedy plant species that one is seeking to control or eliminate willhave a characteristic sensitivity, tolerance and mortality to eachmicronutrient. The unique combinations of plant and micronutrient numberin the thousands, however this invention has demonstrated that invasivespecies have lower tolerance and higher sensitivity to micro-nutrientscompared to perennial grass species suggesting many possibleopportunities for invasive plant control using micronutrientapplication. Most work performed to date has been performed using boronin the range of 0.5-50 mg/L as a water soluble plant micronutrient.Water soluble micronutrient ranges for copper, zinc, manganese,molybdenum and chlorine for control of invasive plant species areexpected to be similarly low, yet the precise targets are expected to beunique to each land area and species targeted. In the instance whereexisting soil micronutrients are near normal levels prior to treatmentto control invasive species target application rates may be lower (e.g.0.01-0.5 mg/L). The selection of a specific micronutrient andapplication rate will be made based on species specific sensitivity toeach micronutrient and cost for each micronutrient fertilizer.

In an illustrative example of the applicability of the invention toother micronutrients, plant community response to water soluble traceelements has been observed at the Anaconda Smelter Superfund site inAnaconda, Mont. At this site, uncontrolled releases of hazardoussubstances from the operation of a copper smelter have resulted in sharpgradients in soil concentrations of water soluble copper and zinc.Immediately adjacent to the smelter stack (where the releasesoriginated) soil levels of water soluble copper and zinc are highest andwith increasing distance from the smelter stack soil levels of copperand zinc decrease. Along the gradient of water soluble copper and zincpresent in the soil, plant community zonation is observed with plantsexhibiting tolerance to highly elevated copper and zinc found close tothe smelter stack and plants with low tolerance to water soluble copperand zinc found only a great distance from the smelter. Perennial grassspecies, for example, appear to be tolerant of elevated soil copper andzinc compared to native forbs which are not found near the smelterstack. In the case of dandelions (an invasive plant species), healthyfields of dandelions are found in uncontaminated soils a distance fromthe smelter. A short distance closer to the smelter, dandelions are verystressed with black leaf spots and reddish leaf margins. Dandelions arenot found where moderate to high levels of water soluble copper and zincare measured in the soil. In contrast the invasive plant species spottedknapweed is found growing in soils with low to high levels of watersoluble copper and zinc, suggested differential and elevated toleranceof copper and zinc compared to dandelion.

This invention is also different than the typical herbicidal applicationof organic chemical formulations to the leaf tissue of growing plantswhere disruption of plant physiological processes is intended to occurin a short period of time (days-weeks) resulting in death of the plant.Control of weedy plant species through changing the levels of inorganicsoil micronutrients (this invention) is intended to restore nutrientlevels in disturbed soil typical of the pre-disturbance condition andalso restoring the soil's natural ability to recycle plantmicronutrients and to preclude weed colonization by maintaining levelsof micronutrient fertility harmful to early-successional plant species(weeds) and beneficial to later successional desirable plant species.Disruption of growing plant physiology through application on live planttissue is not intended. The subject invention is also more likely tohave effect over longer periods of time (months-years) as plantmicronutrients are made available to plants through root uptake ratherthan foliar uptake. If foliar micronutrient uptake occurs duringapplication of liquid micronutrient formulation, some measure ofinvasive species control may occur, yet this is ancillary to the maintreatment effect caused by seed or root uptake from the soil.Additionally, herbicidal application of organic chemicals is often anannual process as new plants grow from seed. In the subject invention,the phytotoxic control of weeds by micronutrient application is aone-time application intent on restoring soil health, plant communitycomposition and long-term control of weeds through natural micronutrientcycling. Subsequent micronutrient applications may be required if targetsoil levels are not attained during a first application due to landscapefactors, climate, grazing, fire or related land management activities.Multiple applications of micronutrients are not prohibited by thisinvention.

The present invention also exploits the life cycle of weedy plantspecies that rely on prolific seed production and dispersion mechanismsto colonize disturbed and nutrient-depleted sites. In particular, annualweedy plant species must grow from seed to maturity every year toperpetuate the plant's life cycle. By creating phytotoxic soilconditions through micronutrient application (this invention) in theuppermost soil layers (˜1 inch depth) weed seeds and seedlings arekilled during or immediately following germination therein preventingthe plant from growing to maturity and producing seed to sustainsubsequent generation of plants. Existing desirable perennial plantspecies are unharmed due to deeper roots which are not exposed tophytotoxic surficial micronutrient levels. Over a period of months oryears the surface applied micronutrients will reach roots in the deepersoil at diluted concentrations which are expected to have a beneficialfertilization affect due to prior nutrient depletion caused by landdisturbance. Many disturbed sites are both water limited due to climateand nutrient limited due to soil depletion. The resulting ecologicallift is caused by the combined effect of enhancing existing desirablevegetation and diminishing the frequency and extent of weedy plants.

In the embodiment of creating a phytotoxic boron solution, having aboron concentration ranging from 0.01-50 milligrams (mg) or,alternatively, 0.5-50 milligrams (mg) soluble boron per liter (L) iscreated by dissolving boric acid, sodium borate, sodium tetraborate, ordisodium tetraborate, or other soluble sources of boron, in water oralternative liquid to create a boron-containing solution.

Thus, in some embodiments of the present invention, the boron or othermicronutrient concentration for use in the present invention ranges asfollows and also includes any/all concentrations between theseconcentrations (all in mg/L): 0.01; 0.02; 0.03; 0.04; 0.05; 0.06; 0.07;0.08; 0.09; 0.10; 0.15; 0.20; 0.25; 0.30; 0.35; 0.40; 0.45; 0.50; 0.55;0.60; 0.65; 0.70; 0.75; 0.80; 0.85; 0.90; 0.95; 1.00; 1.50; 2.00; 2.50;3.00; 3.50; 4.00; 4.50; 5.00; 5.50; 6.00; 6.50; 7.00; 7.50; 8.00; 8.50;9.00; 9.50; 10.00; 11.00; 12.00; 13.00; 14.00; 15.00; 16.00; 17.00;18.00; 19.00; 20.00; 21.00; 22.00; 23.00; 24.00; 25.00; 26.00; 27.00;28.00; 29.00; 30.00; 31.00; 32.00; 33.00; 34.00; 35.00; 36.00; 37.00;38.00; 39.00; 40.00; 41.00; 42.00; 43.00; 44.00; 45.00; 46.00; 47.00;48.00; 49.00; and 50.00.

In one embodiment, the 5 mg B/L concentration is achieved by dissolving29.4 mg boric acid in 1000 milliliters of water. In another embodiment,the 20 mg B/L concentration is achieved by dissolving 117.6 mg boricacid in 1000 milliliters of water. In each case, the solution isthoroughly mixed to assure complete dissolution of the boron. Thesolution is then applied as an aerial spray to the target area. Thesolution is applied to the surface of soil containing invasive speciesseed, directly to weed seed, or to senesced or live, seed-bearing weedplants at a rate of 2-200 milliliters per square meter. A target areamay be any plant community where invasive species are present, e.g.urban land, rangeland, forestland, roadside, brownfield, or disturbedland.

As used herein, the phrase “urban land” refers to an area having thecharacteristics of a city or otherwise developed for human habitation,with intense development and a wide range of public facilities andservices.

As used herein, the term “rangeland” refers to an expanse of landsuitable for livestock or wildlife to wander and graze on.

As used herein, the term “forestland” refers to a section of landcovered with forest or set aside for the cultivation of forests or aswildland without silvicultural intent.

As used herein, the term “brownfield” refers to a piece of industrial orcommercial property that is abandoned or underused and oftenenvironmentally contaminated, especially one considered as a potentialsite for redevelopment.

As used herein, the phrase “disturbed land” refers to land that has beenphysically disturbed by resource operations (e.g., from mining, loggingor construction) that cannot be used for other purposes (e.g., foragriculture or home sites). Disturbed land may be caused by, but notlimited to, grazing by wildlife and domestic animals, fire, roadconstruction, climate change, flooding, landslide, erosion, invasivespecies colonization, tillage for agriculture, urbanization, pipeline orutility installation, dam building (or removal), and the like.

In some embodiments of the present invention, the target area does notinclude land under intensive agronomical or horticultural production.For example, in some embodiments of the present invention, the targetarea does not include land being used to grow row crops, such as is usedfor large-scale growing of soybeans, maize/corn, cotton, dry peas andthe like. In other examples, in some embodiments of the presentinvention, the target area does not include land being used to growtruck crops (i.e., large-scale vegetable crops), such as is used forlarge-scale growing of watermelons, fresh peas, peppers, cucumbers,tomatoes, onions and the like. In still other examples, in someembodiments for the present invention, the target area does not includeland being used to grow large-scale production of flowers, such as isused for large-scale growing of tulips, daffodils, chrysanthemums andthe like.

When applied as a dry, spreadable powder, the specific source of boronis crystalline, powdered boric acid, or other boron-containing compoundsand/or fertilizers. In an embodiment of dry boron application in dryflowable form, 1.98 g boric acid per square meter is applied to thetarget area. Other excipients can be added to the formulation to enhanceor ensure the composition remains flowable to the desired consistency.The dry flowable form is applied to the surface of soil containing weedseed, directly to weed seed, or to senesced or live, seed-bearing weedplants.

Applying a boron-containing formulation to weed seeds, weed seedlings,and/or weed plants functions by disrupting the target species cellphysiology when moisture containing boron is imbibed by the seed orseedling from the soil. While control of invasive plant species is theoutcome of the invention, the applications of micronutrients areintended to change the soil chemistry. The soil is the host of themicronutrients delivered to the invasive plant species. In eachapplication embodiment, whether liquid or dry, the applied boron is madeplant-available either through dissolution by rainfall, snowmelt orother environmental conditions, or plant uptake of the liquidapplication, and is therefore plant-available regardless of the form ofapplication. The actual mechanism of boron involvement in plantphysiology remains somewhat unclear. There is a very narrow windowbetween the levels of boron required by and toxic to plants. The subjectinvention discloses the specific, narrow window of concentrations ofboron toxic to invasive plant species, thereby allowing control byapplication of boron concentrations in excess of invasive plant speciestoxic limits, yet below levels toxic to desirable species.

Another embodiment of the invention entails measuring the amount ofplant-available boron in the soil in the target area and addingsupplemental boron to achieve an effective level harmful to invasiveplant species, but not harmful to desirable vegetation (also referred toas the Induced Phytotoxicity Threshold or IPT). Under this embodimentthe naturally occurring soil boron level is measured thereinestablishing a baseline boron concentration. This method is madepossible by laboratory, greenhouse and field testing of common plantspecies and development of unique characteristic dose-response curvesidentifying plant growth characteristics resulting from varying thewater soluble boron concentrations across the range of 0.5 to 50 mg/L.The novel finding that facilitates the invention is the sensitivity ofinvasive plants species to low levels of water soluble soil boroncompared to desirable plant species found on rangeland or otherenvironments.

Each of the embodiments of the present invention as described herein forpreparation and application of boron are similarly applicable toformulations containing the other micronutrients useful for thisinvention. Such formulations containing the other micronutrients, orcombinations thereof, may be similarly prepared and applied to a targetarea, depending on the invasive species that is to be controlled oreradicated and the IPT for that species, micronutrient and target areasoil conditions or preexisting micronutrient levels.

Boron toxicity to invasive plant species appears to cause significantchanges in the physiology and activity of numerous enzymes in seed andseedling development, and consequently plant metabolism during the lifecycle of the plant. Three main candidates for boron toxicity involve theability of boron to bind compounds with two hydroxyl groups in thecis-configuration: (a) alteration of cell wall structure; (b) metabolicdisruption by binding to the ribose moieties of molecules such asadenosine triphosphate (ATP), nicotimamide adenine dinucleotide; and (c)disruption of cell division and development by binding to ribose, eitheras a free sugar or within RNA. However, the only defined physiologicalrole of boron in plants is as a cross-linking molecule involvingreversible covalent bonds with cis-diols on either side of borate.Because boronic acids cannot cross-link two molecules, the addition ofboronic acids causes the disruption of cytoplasmic strands andcell-to-cell wall detachment. Boronic acids appear to specificallydisrupt or prevent borate-dependent cross-links important for thestructural integrity of the cell, including the organization oftransvacuolar cytoplasmic strands. Boron likely plays a structural rolein the plant cytoskeleton.

Many variations of the invention will occur to those skilled in the art.Some variations include plant micronutrients in addition to or in placeof boron. Known plant micronutrients include boron, copper, zinc,manganese, iron, chlorine and molybdenum. Other variations call forvariations and ranges of the concentrations of each element beingapplied, and the compound source for the micronutrient. See, e.g., Table1 supra. Other variations include application of combinations of morethan one plant micronutrient. Other variations include application ofmicronutrients with macronutrients nitrogen (N), phosphorous (P) orpotassium (K). Additional variations include the targeted invasive plantspecies subject to control or eradication. Additional variations includethe type of site or landscape the methods and compositions of thisinvention may be applied to. There are many different techniques whichmay be used to apply or distribute a specific form of the compounds(whether liquid or dry). The application rate can be adjusted across arange from low to high concentration to reduce, control, andeliminate/eradicate a particular invasive plant species or species. Theapplication rate can be adjusted and applied to protect against futureinvasion by invasive species. The application rate can also be appliedat such levels to cause a phytotoxic condition for all plants resultingin bare ground. All such variations are intended to be within the scopeand spirit of the invention.

Although some embodiments are shown to include certain features orsteps, the applicant specifically contemplates that any feature or stepdisclosed herein may be used together or in combination with any otherfeature or step in any embodiment of the invention. It is alsocontemplated that any feature or step may be specifically excluded fromany embodiment of the invention.

The utility of this invention is multi-fold and includes but is notlimited to the following uses:

-   a) The invention is useful for control or eradication of invasive    plant species currently occupying more than 100 million acres in the    U.S.;-   b) The invention comprises non-synthetic, non-organic naturally    occurring inorganic earth elements, which are known plant nutrients,    non-carcinogenic and non-impairing to soil and water resources at    the low concentrations involved in this invention;-   c) The invention comprises relatively inexpensive, easily accessible    materials, combined with relatively simplified methods of    utilization;-   d) Boric acid, borate salts or boron (and the other micronutrients    of the invention) are neither classified as endocrine disruptors nor    are they currently on the list of compounds being screened by the    U.S. EPA as part of the Endocrine Disruptor Screening Program (EDSP)    for potential in humans;-   e) Boric acid and borate salts (and the other micronutrients of the    invention) are classified by the U.S. EPA as “not likely to be    carcinogenic to humans” under the 2005 carcinogen assessment    guidelines;-   f) There is no reported risk from occupational exposures studies    indicating the carcinogenicity of boric acid, borate salts or boron    (and the other micronutrients of the invention);-   g) The effectiveness and use of the subject invention is facilitated    by the application of relatively small/minute amounts of material    required to treat large areas of land;-   h) The invention is specifically selective to weedy plant species,    allowing the invention to be used on land parcels of mixed plant    communities without significant adverse impact on desired plant    species;-   i) The invention allows for application of low concentrations of    micronutrient-containing compositions to plants, seeds, seedlings or    soil which results in phytotoxic responses of weedy species while    minimizing impact to existing desirable native plant species.

The methods of the present invention use micro-nutrients required insmall amounts by most vascular plants, as an herbicide or chemical agentagainst invasive plant species. The formulations of the inventioneffectively cause the death of live plant, seedlings, or seeds ofinvasive plant species, when the soluble trace element comes in contactwith germinating seed or are taken up by the roots of live plants.Similarly, the formulations of the invention effectively cause the deathof seedlings of invasive plant species, when the trace element comes incontact with the emerging seedlings. The findings of the inventor areunexpected and surprising. One skilled in the art may expect that basedon scientific literature and accepted agronomic practices that theaddition of micro-nutrients to soil for uptake by plants would enhanceplant performance of all species, rather than cause selective death toseed, emerging seedlings or live plants. Also surprising, theapplication of relatively low concentrations of micronutrient-containing formulations which are phytotoxic to invasivespecies do not result in harm to desirable native species, or at leastare less harmful over a spectrum of desirable native species. Theinvention provides a significant new tool and method for land managersto effectively control or eradicate invasive species over a wide varietyof acreages and may be modified to suit site conditions, includingspecific plant communities. The low rates of application are alsomanifested in low unit cost per land area treated.

Although scientific literature reports instances of trace elementtoxicity to vascular plants, these instances of toxicity typically haveoccurred in response to unusually high concentrations of trace elements.The inventor is not aware of any prior art wherein trace elements, inminute quantities, are used for the specific purpose of plant, seed orseedling death of unique species, i.e., constituting ‘weed control’. Ofthe sixteen chemical elements known to be important to a plant's growthand survival, thirteen come from the soil, are dissolved in water andabsorbed through a plant's roots. In some instances, there are notalways enough of these nutrients in the soil for a plant to growhealthy. In other instances, some combinations and concentrations ofthese nutrients, particularly the micronutrients, can be detrimental ortoxic to some plants. Micronutrients, those elements essential for plantgrowth and which are needed in only very small (micro) quantities, areboron (B), copper (Cu), iron (Fe), chlorine (Cl), manganese (Mn),molybdenum (Mo) and zinc (Zn). These micronutrients play critical rolesin carbohydrate transport, metabolic regulation, osmosis and ionicbalance, enzyme and chlorophyll synthesis and function, internalchemical transformations, and cell reproduction/division.

Extensive research has documented that plants are often sensitive torelatively minute concentrations or exposures to unique syntheticcompounds or combinations of naturally occurring elements, includingmicro-nutrients. For example, glyphosate (aka ROUNDUP®, a syntheticMonsanto product) is effective at causing photosynthetic disruption inchlorophyllitic plants at an application rate of as little as 0.75pounds active ingredient per acre, which equates to only approximately 8mg/square foot of application, equivalent to approximately 14 ppmapplication rate. The American Phytopathological Society (APS) reportedthat micronutrients are generally toxic when present in high amounts,although ‘high concentrations’ are not clearly defined, and littletoxicity have been reported at exceptionally low micro-nutrientconcentrations. This occurrence is known as micro-nutrient toxicitysyndrome (MTS). As an example, Jong et al. (1996) reportedmicro-nutrient toxicity in French marigold induced from boron, copper,iron, manganese, molybdenum, and zinc at concentrations of 0.5, 4, 2, 1and 5 mg/L, respectively. In addition, plants can vary considerably fromspecies to species in their susceptibility to nutrient toxicities. Forexample, Lee and others (1996) reported inducing seed geranium(Pelargonium×hortorum) micronutrient toxicity symptoms by applyingnutrient solutions containing 0.5 mg/L B, Cu, or Zn, or as little as0.25 mg/L Mo, in combination with nitrogen, phosphorus, and potassium.Micronutrient toxicity has also been reported for Begonia,Chrysanthemum, Geraniums, Marigolds, Poinsettia, and Lilium longiflorum(Hammer et al. 1987; Jong-Myung et al. 1996; Lee et al. 1996; Marousky,1981).

The toxic effects of excessive application of nutrients to agriculturaland horticultural crops are well documented. Even the macronutrientnitrogen can be toxic to plants if applied in excess. Similarly,excessive application of micro-nutrients can cause phytotoxic effects.However, excessive micronutrient concentrations are rarely found innative soils, with the exception of mineralized areas. In mineral soils,release of micronutrients is usually quite slow. Much of the availablesoil micronutrients are held rather tightly by soil organic material andthus toxicity to plants is not a frequent occurrence under ‘field’conditions. For the majority of landscape plants micro-nutrientconcentrations in the saturated soil paste extract between 0.15-0.5parts per million are desired. Depending on plant sensitivity, some ofthese elements can be toxic at soil test concentrations above one partper million. Nutrient toxicity does not often occur in most arablesoils. Such toxicity exerts different effects on very diverse processesin vascular plants, such as altered metabolism, reduced root celldivision, lower leaf chlorophyll contents and photosynthetic rates, anddecreased lignin and suberin levels, among others (Nable et. al. 1997;Reid 2007b). Accordingly, reduced growth of shoots and roots is typicalof plants exposed to high micro-nutrient levels (Nable et al. 1990).Referring to Keren and Bingham (1985), safe concentrations ofmicro-nutrients in irrigation water range from 0.3 mg/L for sensitiveplants [i.e. avocado (Persea americana), apple (Malus domestica) andbean (Phaseolus vulgaris)], 1-2 mg/L for semi tolerant plants [oat(Avena sativa), maize (Zea mays), potato (Solanum tuberosum)], and 2-4mg/L for tolerant plants [i.e. carrot (Daucus carota), alfalfa (Medicagosativa) and sugar beet (Beta vulgaris)].

Sensitivity of cheatgrass (Bromus tectorum), dandelion (Taraxacumofficinale), spotted knapweed (Centaurea maculosa) and other weedyspecies to micro-nutrients has not been reported in the scientificliterature. The literature identifies boron, copper, zinc, manganese andmolybdenum as potential plant toxins at ‘elevated’ concentrations uniqueto each species. The literature does not suggest a method forselectively controlling undesirable plant species (i.e. weeds) byapplication of micro-nutrients above the phytotoxic threshold for thatspecies.

Current techniques used for invasive plant species control are largelylimited in their effectiveness as they are indiscriminately harmful toall existing vegetation to which they are applied (i.e. glyphosate), orare harmful to non-target species to which they are applied of the samelife form as the invasive species (i.e. collateral damage to forbs with2,4-D application). The fertilizer and weed control industries aremulti-billion dollar entities. Invasive plant management is a pervasiveproblem on as much as 100 million acres in the U.S., with onlymarginally effective control methods. The methods of the subjectinvention offer a cost-effective means to address invasive plantinvasion and the associated economic losses due to diminished landproductivity, yet without collateral damage to the environment.

EXAMPLES

The invention will now be illustrated in greater detail by reference tothe specific embodiments described in the following examples. Theexamples are intended to be purely illustrative of the invention and arenot intended to limit its scope in any way.

Example 1

Field trials were established in existing perennial grass communitiesnear Belgrade, Mont., with high levels of cheatgrass and dandelioninvasion into existing perennial grasses to examine use of boron(elemental symbol: B) fertilization for weed control. Minute amounts ofboron, in doses as low as 5 mg B/L (soluble) or 2-3 lbs B (dry) activeingredient per acre, were applied to the plots.

Subsequent observations in following growing seasons confirmed thenear-total absence of either emerging or mature cheatgrass plants inthese plots, with a return to perennial grass dominated community over a5 year period using a single application of boron fertilizer. Over thesame period of time dandelion cover decreased from a mean of 59% to 15%,and cheatgrass cover decreased from a mean of 47% to 1%, while perennialgrass cover increased from 42% to 71%.

FIG. 1A presents the mean dandelion, cheatgrass and perennial grasscover over 5 growing seasons to applications of dry formulations ofboron fertilizer.

FIG. 1B presents the mean dandelion, cheatgrass and perennial grasscover over 5 growing seasons to applications of liquid formulations ofboron fertilizer.

Example 2

Greenhouse petri dish experiments were completed to evaluate the effectof minute concentrations of boron on cheatgrass seed germination.Treatment concentrations (in addition to a zero treatment control)ranged from 10 to 50 mg B/L dissolved in distilled water. Controltreatments germinated at 100% within 5 days (FIG. 2A), while all of theseed treated with boron exhibited zero percent germination after 14 days(FIG. 2B). A follow-up experiment, essentially repeating the previouslydescribed petri dish experiment, with inclusion of a treatment rate aslow as 5 mg/L, was completed. It was observed that cheatgrass seedsgerminated at the 5 mg/L concentration, with death of the seedlingsoccurring within 7 days of germination (data not shown).

Example 3

In a greenhouse pot study Kentucky bluegrass, bluebunch wheatgrass,cheatgrass, dandelion and spotted knapweed were grown from seed inpotting soil for a period of approximately 26 weeks. Plants were wateredwith tap water for the first 24 weeks and then 3 times with boronsolutions during the final 2 weeks of the study. Boron concentrationsused were 5, 10, 25 and 50 mg B/L in addition to a tap water treatmentand a commercial plant fertilizer solution.

FIG. 3A shows the phytotoxic response to dandelion resulting fromwatering with boron solutions, while FIG. 3B shows a similar response tospotted knapweed. Both species showed marked phytotoxicity at the lowestboron solution concentration used (5 mg B/L).

FIG. 3C shows the minimal effect to a desirable rangeland grass species(bluebunch wheatgrass) to the same solutions. Bluebunch wheatgrass wasable to tolerate concentrations of boron at or above 50 mg B/L.

FIG. 3D shows the response of Kentucky bluegrass, cheatgrass, dandelion,bluebunch wheatgrass and spotted knapweed to the 10 mg/L boron solution.Responses varied across species at this concentration.

Example 4

Rangeland site cheatgrass plant cover over a five-year study period inresponse to water soluble boron concentrations in soil resulting fromsurface liquid boron applications. Perennial grass densities wereobserved to increase over time in the treated area, while the adjacentnative range site remained weedy with abundant cheatgrass cover (FIG.4). Soil sampling of the 0-6 inch depth was performed annually todetermine the water soluble boron concentrations both in the treated anduntreated areas. Transects were used to measure plant cover annually atsites co-located with soil sampling.

Example 5

At a cheatgrass-affected rangeland site plant cover over a two-yearstudy period is shown in response to water soluble soil boronconcentrations resulting from surface liquid boron applications.Perennial grass cover in the treated rangeland site was increased tobetween 60 and 70 percent cover while cheatgrass cover decreased and wasless than 3% (FIG. 5A) while adjacent untreated rangeland had lessperennial grass cover and more cheatgrass after 2 years. (Soil samplingof the 0-6 inch depth was performed annually over a five year period todetermine the water soluble boron concentrations both in the treated anduntreated areas (FIG. 5B). Transects were used to measure plant coverannually at sites co-located with soil sampling.

Example 6

Plant color and vigor were measured in a small pot greenhouse study inresponse to solutions of increasing boron concentration, as reflected ina plant health index (same study as example 2 above). Bluebunchwheatgrass is a desirable native perennial grass common in rangeland ofthe western U.S. and a primary forage species of livestock and wildlife.Bluebunch exhibited little change in plant health with increasing boronconcentrations while cheatgrass, dandelion, spotted knapweed andKentucky bluegrass plants declined in vigor. Spotted knapweed showed themost rapid decline in plant health with increasing solution boronconcentration. Spotted knapweed is commonly listed as a noxious weed byState agencies in the western U.S. Spotted knapweed commonly invadesbluebunch wheatgrass plant communities in western Montana, and elsewherein the western U.S. These results suggest micro-nutrient fertilizationwith boron solutions could be used to control spotted knapweed whileallowing persistence of bluebunch wheatgrass. Greenhouse pot irrigationstudy, Bozeman, Mont. (FIG. 6).

Example 7

Greenhouse evaluation of live/near-mature cheatgrass plant response towatering with increasing concentrations of boron-containing solutions,compared to watering with tap water (FIG. 7).

Seed initially germinated in potting soil watered with tap water forfour months, after which watering with treatment solutions wasinitiated.

Pots watered with treatment solutions 3 times per week for two weeks,after which plant health index (product of qualitatively assessed plantcolor and vigor) was determined.

Example 8

Germination percentage of cheatgrass, dandelion, spotted knapweed andKentucky bluegrass seed was measured ten (10) days after treatment withsolutions of increasing boron concentration (FIG. 8). Cheatgrassappeared most sensitive to boron solution resulting in essentially 100%death of 20 cheatgrass seeds in covered petri dishes, when treated withsolutions with boron concentration ranging from 5 to 50 mg/L. Controltreatment using tap water successful germination percentage exceeded56%.

Very little germination was observed by any species when boronconcentrations reached 25 mg/L.

Example 9

In an illustrative example the micro-nutrient requirements for twounique species are shown: an invasive plant species and a desirableplant species. See FIG. 9.

The dose-response curves show plant deficiency at low concentration,maximum plant biomass production at unique moderate concentrations andphytotoxic species-specific responses at higher concentration. In thisexample, and based on supporting observations, invasive plant specieshave lower tolerance to elevated micro-nutrient levels. Each invasivespecies and desirable species is believed to have a uniquemicro-nutrient requirement, yet the invasive species may be controlledthrough micro-nutrient addition at the Induced Phytotoxicity Threshold(IPT) where the invasive species is reduced in vigor and distributionwhile the desirable species is unharmed or even stimulated by abeneficial micro-nutrient fertilization response. The short-term landmanagement objective is to swiftly eradicate invasive plant species. Thelong-term land management objective in this plant-soil system is torestore and sustain micro-nutrient levels at the Induced PhytotoxicThreshold by balancing micro-nutrient inputs with withdrawals tomaintain a long-term equilibrium micronutrient level phytotoxic toinvasive plant species. It is believed that disequilibrium has beencaused to many plant-soil systems by decreasing the levels of soilmicro-nutrients through anthropogenic land management practicesresulting in a net removal of soil micronutrients leading to increasedsusceptibility to invasive species colonization. In this invention, soilmicro-nutrient levels are restored to pre-disturbance levels and soilhealth is re-invigorated leading to promotion of the desired plantspecies and minimization of the presence of invasive plant species.

Example 10

Formulation examples for invasive plant species (cheatgrass) ascontrolled by micronutrient (boron):

Formulation A, rate 1: dry granular boron-containing component 0.005882%by weight, water 99.99412% by weight. Thoroughly mix until completelydissolved, apply to target area containing mature cheatgrass, cheatgrassseedlings, or cheatgrass seed. This formulation can also be applied to atarget area as a dry formulation, without mixing with water, and allowedto dissolve naturally through environmental conditions (precipitation)for uptake by cheatgrass plants, seedlings or seeds.

Formulation B, rate 1: dry granular boron-containing component 0.006666%by weight, water 99.99333% by weight. Thoroughly mix until completelydissolved, apply to target area containing mature cheatgrass, cheatgrassseedlings, or cheatgrass seed. This formulation can also be applied to atarget area as a dry formulation, without mixing with water, and allowedto dissolve naturally through environmental conditions (precipitation)for uptake by cheatgrass plants, seedlings or seeds.

Formulation C, rate 1: dry granular boron-containing component 0.007142%by weight, water 99.99286% by weight. Thoroughly mix until completelydissolved, apply to target area containing mature cheatgrass, cheatgrassseedlings, or cheatgrass seed. This formulation can also be applied to atarget area as a dry formulation, without mixing with water, and allowedto dissolve naturally through environmental conditions (precipitation)for uptake by cheatgrass plants, seedlings or seeds.

Formulation D, Using the boron-containing compound Na₂B₄O₇.10H₂O, the0.5 mg/L soil concentration applied in the field experiment described inExample 1 was attained by adding 2.55 grams per 100 square foot. The 50mg/L soil concentration was attained by adding 255 grams per 100 squarefeet. These concentrations were applied either dry or by dissolving theboron-containing compound in water and then applied as a liquid to fieldplots. The resulting data are shown in FIGS. 1A and 1B.

Example 11

Exemplary formulations for the micronutrient, boron, are outlined inExample 10; however each formulation can be similarly made with theother micronutrients of this invention at a specified concentration toachieve the IPT for the selected invasive species.

Example 12

On disturbed land (which may include degraded rangeland, mine land,roadside, brownfield, logged land, etc) in much of the western US,cheatgrass has become a dominant species displacing desirable nativevegetation. Using a helicopter, tractor or similar dispensing method amicronutrient formulation containing boron (alternative: copper,manganese, zinc, etc) can be applied to the soil surface during theperiod of August awaiting fall precipitation and germination. The amountof water soluble and plant available boron will vary depending on thesite soil and invasive species present, but might be in the range of0.35-14 pounds of plant available boron per acre (e.g. 2.4-98 pounds peracre of boron fertilizer containing 14.3% boron). Alternativeformulations could be developed using copper, zinc, manganese,molybdenum, chlorine and iron.

Upon adequate rainfall the micronutrient fertilizer will be dissolvedand enter the soil where cheatgrass seeds will be found on the soilsurface or near the soil surface. Under conditions of adequate moistureand soil temperature the cheatgrass seeds will germinate and begin togrow using stored carbohydrates in the seed. It is known by thoseskilled in the art that above ground plant growth is matched by belowground root development. Encountering micronutrients in the soil as aresult of surface application, the plant roots will take up thenutrients which disrupt normal plant growth resulting in death of theemerging seedling. This type of response normally occurs inSeptember-October as cheatgrass is a winter annual plant (although, itcould happen anytime there is soil moisture, heat, cheatgrass seed—notin the winter and not during the period of active plant growth). In thespring remaining cheatgrass seed in the soil will encounter phytotoxicconcentrations of micronutrients and perish. The removal of the annualplant would allow for more soil resources to go toward existingdesirable plant species (e.g. bluebunch wheatgrass, Western wheatgrass,Idaho fescue, big sagebrush) and allow for establishment of desirableplant species which naturally exhibit greater tolerance to soilmicronutrients compared to annual weeds.

Following the procedure set forth herein, the expected end result willbe greatly diminished cheatgrass cover and the greater establishment ofmore desirable species leading to better forage for livestock andwildlife. For example, cheatgrass cover prior to treatment might rangefrom 5-25% cover while desirable perennial grass cover might range from25-35% plant cover; following micronutrient application cheatgrass coveris anticipated to decrease to less than 1% cover while perennial grasscover increases to 40-60% plant cover. In this example the desirableforage available for livestock and wildlife would increase 37-41%.

Following this procedure should result in a near-permanent soiltreatment provided nutrient cycling continues to occur through goodrangeland stewardship (i.e., not allowing overgrazing). Maintenance ofthe desired outcome requires mass balance, i.e., the nutrients inputmust balance with nutrients removed.

Example 13

In another example, for a roadside where cheatgrass may becomeestablished during a road widening project, the State Department ofTransportation would hire a contractor to apply a liquid formulation ofmicronutrient fertilizer using a backpack sprayer along the roadside tocontrol cheatgrass invasion. The conventional practice typically usedprior to this invention was to spray an indiscriminant vegetationelimination compound (e.g. Roundup) around the base of each roadsidedelineator to facilitate mowing. Using the conventional Rounduppractice, where Roundup is applied, cheatgrass invasion would result thefollowing year due to the disturbance (elimination of plant cover),assuming that a cheatgrass seed source is available. Alternatively, theuse of the micronutrient soil treatment will eliminate the growth thecheatgrass and allow for reestablishment of other more desirable grassor other plant species either through natural recolonization or throughreseeding.

In the case where the Departments of Transportation desire a zone clearof vegetation around each highway delineator, a higher rate ofmicronutrient fertilization (˜10× normal cheatgrass suppression ratesfor rangeland) could be applied to cause long-term elimination ofcheatgrass. This technique would be an alternative to using Roundup toeliminate all vegetation. Roundup has to be applied annually. Longerterm protection from weed encroachment is likely with this micronutrienttechnique.

Example 14

Near an oil well pad in southern Wyoming the soil is disturbed duringdrilling and development of the well. Under permit the oil company isrequired to reclaim the site. In this example, weed management forcheatgrass is a significant problem for these types of sites.Micronutrient fertilization would be applied to restore soil health andprevent weed colonization. Using this method, a soil sample will becollected of a near-by undisturbed site with healthy vegetation. Thesoil levels of micronutrients will be measured by a laboratory. Thelevels of soil micronutrients will also be measured in the disturbedsoil. A prescription may then be developed to apply amounts of boron,copper, zinc and manganese to the disturbed site to bring themicronutrient levels in the disturbed soil to or near the levels thatare measured in the near-by undisturbed site. The site may then beseeded with native plant species appropriate to that location andconcurrently fertilized with the soil micronutrient prescription,resulting in the return of healthy vegetation cover on the oil well padsite, absent weeds.

Example 15

In a Kentucky bluegrass lawn in Chicago dandelions have become wellestablished but the landowner is disinclined to use 2-4D herbicidalcontrol methods. A Copper-Boron-Nitrogen fertilizer would be applied tothe lawn at rates harmful to dandelions yet beneficial to Kentuckybluegrass resulting in diminished dandelion cover (reduced from 60%cover to 15% cover over 4 years following a single application) andincreased bluegrass growth and vigor.

Example 16

In the Bitterroot Valley of western Montana elk herds may be decliningin number due to reduced forage availability caused by rangelanddegradation by a perennial noxious weed—spotted knapweed. Nearbylivestock grazing operations experience similar losses in production.Fields invaded by knapweed have been sprayed annually by aconservation-minded landowner at a cost of $300/acre/application. Thelandowner has tried several herbicidal treatments (such as 2-4-D andother traditional formulations) with varying success, but the centralproblem is that while the herbicide kills 100% of the knapweed it isapplied to a new generation of plants that germinates from seed reservesin the soil (knapweed seed may survive for decades) or new seed is blownin from the neighbor's property. The landowner is frustrated at the highcost and recurring problems from noxious weeds.

In this example of the invention, after traditional herbicideapplication to kill the mature perennial plants, a micronutrientapplication of boron would be surface applied as dry fertilizer using atractor and PTO mounted flail spreader. The boron application would beapplied in September on a dry year (low natural precipitation) and noknapweed seed germination would be expected to be observed in the fallprior to winter. Snowfall and spring rain following the treatment woulddissolve the micronutrient application which would result in elevatedlevels of boron in the upper layer of soil containing invasive speciesseed.

Resident knapweed seed would be expected to germinate the following Mayin response to soil temperature and moisture. The germinating seed wouldput down an incipient root and surface dicot leaves as the plant beginsto become established. However, in this example, unlike priorgenerations, the young knapweed plant would encounter elevated boronlevels in the surface soil which would be phytotoxic to its growth. Amajority of the young knapweed plants would die (some may germinategiven a potentially non-uniform application of the boron treatment). Theexisting perennial grass plants are deep rooted and tolerant of boronand would be unharmed. Prior to treatment, the boron levels in the soilwere lower than desired for perennial grass production, so followingtreatment a beneficial plant growth response would occur on the site.The net result would be long-term protection of the land from spottedknapweed germination and establishment, reduced weed control costs,increased forage production, and more elk.

Example 17

In this example, in Western North Dakota leafy spurge, a noxious weedthat is difficult to control due to its extensive underground rootsystem, has become well established. Application of traditionalherbicide to the above ground leaf surfaces is successful in controllingthe growth of leafy spurge during the year of herbicide application.However, the plant routinely resprouts the following season from rootsunharmed by the herbicide since the herbicide did not translocate to theroots. Recognizing the invasive plant strategy of aggressively competingfor soil nutrients an application of nitrogen, copper and boron will beapplied in April—early in the growing season. Heavy spring rain woulddissolve the fertilizer which can then be taken up by the plant rootsystem, which recognizes the nutrients yet has no physiological controlsfor limiting uptake of phytotoxic concentrations.

The application and following uptake by leafy spurge plants would resultin harm to the leafy spurge, including death of many of the leafy spurgeplants. Additionally the resulting soil surface will be phytotoxic toleafy spurge seeds.

The soil will be reseeded with native and introduced plant seedstolerant of the elevated micronutrient levels (primarily grasses such assmooth brome, western wheatgrass and timothy).

After a period of years, the site would be reseeded with appropriatenative and introduced forbs (such as blue flax, alsike clover andalfalfa) which while somewhat tolerant of elevated soil Boron/Copper thesite would require 2 to 7 years of equilibration prior to reachingnon-toxic levels for the native forbs. The leafy spurge meanwhile wouldfail to recolonize the site due to its seed sensitivity to the soiltreatment and eventually due to a lack of nearby seed source.

Example 18

In this example a severely burned rangeland site has become colonized byinvasive plants which have reproduced for several years, accumulating asubstantial seed bank of invasive plant seed. In addition to losses ofsoil micronutrients, the soil organic matter was also lost due to theintense heat of the fire and with it the primary source of macronutrientnitrogen. U.S. Forest Service and Bureau of Land Management experiencewith similar sites suggest that reseeding with native grasses is oftenunsuccessful due to the low nutrient levels and intense competition forsoil resources by invasive plants. Addition of nitrogen throughfertilization only makes the invasive plants grow larger and havinglimited affect on the few desirable species present. In this futureapplication of soil micronutrients, application is performed in twosteps.

In the first step, boron fertilizer would be applied early in the springprior to plant growth and at rates phytotoxic to invasive plants seeds,to established mature invasive plants and to young germinating invasiveplants. The goal of the first step (step 1) is to greatly diminish theplant cover of invasive plant species and to kill many invasive plantseeds. In the fall of the same year the site would be reseeded (dormantfall seeding) with desirable native plant species (primarily perennialgrasses such as bluebunch wheatgrass and Idaho fescue). At the time offall seeding a soil sample would be collected to assess themacronutrient (N/P/K) and micronutrient (Cu/Zn/Mn/Mo/Fe/B/Cl) levels inthe soil.

In the early spring of the second year step 2 would be implemented priorto germination of the desirable species seeded. Step 2 would consist ofa second fertilization activity focused on restoring both macronutrientand micronutrient fertility levels consistent with the nutritionalrequirements of the desirable species and based on the soil samplecollected the previous fall. For example, in the hypothetical soil thenitrogen requirement was 22 pounds of nitrate nitrogen per acre, thephosphorous requirement is zero, the potassium requirement is zero, thecopper requirement is 7 pounds per acre, the molybdenum requirement is 2pounds per acre and the boron requirement is 1 pound per acre.

The first step would be a boron-only fertilizer intent on sharplyreducing invasive species, while the second step would be a broadspectrum fertilizer intent on promoting growth of desirable plantspecies.

Example 19

In this example an alfalfa field has become invaded by cheatgrass, aninvasive shallow—rooted annual grass. Alfalfa is deep-rooted and aperennial plant with high phosphorous fertilizer requirements. Alfalfais often tilled up every 5-10 years due to depletion of soilphosphorous. Surface application of phosphorous fertilizer isineffective as it does not leach into the soil profile and must betilled into the soil to be effective. Tillage, fertilization andreseeding of alfalfa are expensive and the quality of forage is madeworse by the presence of cheatgrass and shortening the period of healthyproduction. In this example, we assume cheatgrass increased from a fewpercent cover in the first growing season to 30% cover in the thirdgrowing season—an unacceptable level.

To reduce or remove cheatgrass an application of boron fertilizer wouldbe applied at a rate in the range of 0.35-14 pounds of plant availableboron per acre. Application of boron fertilizer would occur in Septemberafter the first frost (i.e. alfalfa no longer growing) and coincidentwith the end of the irrigation season, yet before potential fallcheatgrass germination.

The expected outcome would be the removal of cheatgrass throughphytotoxic response to soil boron when germinating. In the spring of thefollowing year, nitrogen fertilization could be added to stimulate thealfalfa crop where previously if nitrogen fertilization was added itwould have only benefited the cheatgrass and led to increased cheatgrassbiomass and seed production—exactly opposite of the desired outcome.Alfalfa production is restored and cheatgrass removed through timelymicronutrient application.

Example 20

Sage grouse, a candidate for endangered species listing, is dependent onsagebrush habitat for survival. The preferred sagebrush habitat is amixture of forbs, perennial grasses and shrubs—especially sagebrush.This diverse rangeland habitat provides both hiding cover and forage forsage grouse during its life cycle. However, the sagebrush habitat of thewestern U.S. has become degraded, less diverse and colonized by invasivespecies—particularly cheatgrass. The sage grouse species has sharplydeclined in number and habitat restoration has not occurred due to alack of cost-effective control methods for cheatgrass across millions ofacres.

In this example, sagebrush restoration may be performed by aerialapplication of micronutrient fertilizer in the range of 0.35-14 poundsof plant available boron per acre in August of the growing season priorto fall germination of cheatgrass. Subsequent to control of cheatgrassby micronutrient-induced phytotoxicity, the same rangeland sites wouldbe aerial seeded with desirable native plant species. Recontamination ofboron-treated rangeland sites by wind-blown cheatgrass seed would occur,yet cheatgrass seed would fail to germinate due to the persistence ofphytotoxic levels of plant available boron in the surface soil.Conversely, desirable native plant species would germinate in theboron-treated soil due to their differential tolerance of soil boron.

In this example, large tracts of land could be treated efficientlyresulting in long-term reduction in cheatgrass cover and recolonizationof disturbed sites by desirable plant species. Recovery of the nativevegetation would provide opportunities for sage grouse recovery. Therecovery of the degraded rangeland would be perpetuated through landstewardship which safeguarded both the soil quality and rangeland healthby emphasizing very low intensity grazing intent on recycling soilnutrients.

Example 21

In this example, a rangeland site has become colonized by three invasivespecies. From dose-response testing it can be determined that 2 of theinvasive species can be controlled by boron fertilization while thethird is tolerant of boron, but not zinc. Of the two boron-sensitiveinvasive plant species, one is intolerant to a soil solution level of 3mg boron per liter, while the other is sensitive to 7 milligrams perliter. The zinc-sensitive invasive plant species shows 38% biomassreduction at 0.4 mg zinc per liter and 89% biomass reduction at 0.9milligrams per liter.

A custom blended micronutrient fertilizer could therefore be preparedwhich when applied to the surface soil results in a plant availableboron level of 7 mg per liter and 0.9 mg zinc per liter. The combinedmicronutrient formulation would exploit phytotoxic response of threedifferent invasive species found on the same rangeland site. In thefollowing growing season an observer would expect to find greatlyreduced plant cover of all three invasive plants.

It is understood that there are other embodiments of the invention otherthan that described herein, which is provided to explain the inventionto those skilled in the state of the art and should not be construed aslimiting the claims made below.

ADDITIONAL REFERENCES

-   Bangsund, D. A., and Leistritz, F. L. 1991. Economic impacts of    leafy spurge on grazing lands in the northern Great Plains. NDSU    Agriculture Economic Report No. 275-S.-   Elliott, G. C. and P. V, Nelson. 1981. Acute boron toxicity in    Begonia×hiemalis Schwabenland Red.' Commun. Soil Sci. Plant Annu. 12    (8):775-783.-   Gogue, G. J. and K. C. Sanderson. 1973. Boron toxicity of    Chrysanthemum. HortScience 8:473-475.-   Hammer, P. A. and D. A. Bailey. 1987. Poinsettia tolerance of    molybdenum. HortScience 22: 1284-1285.-   Heap I. 2006. The International Survey of Herbicide Resistant Weeds.    Available from URL: http://www.weedscience.com.-   Jong-Myung, Chun-Ho Pak, and Chiwon W. Lee, 1996. Micro-nutrient    toxicity in French marigold. J. Plant Nut. 19 (6): 901-916.-   Kabata-Pendias, A. and H. Pendias. 2001. Trace Elements in Soils and    Plants, Third Edition. CRC Press.-   Keren R and Bingham F T 1985 Boron in water, soils, and plants. Adv.    Soil Sci. 1, 230-276.-   Lee, Chiwon W., Jong-Myung Choi, and Chun-Ho Pak. 1996.    Micronutrient Toxicity in Seed Geranium (Pelargonium×hortorum    Bailey). J. Amer Soc. Hort. Sci. 121 (1):77-82.-   Marousky, F. J. 1981. Symptomology of fluoride and boron injury in    Lilium longiflorum Thunb. J. Amer. Soc. Hort. Sci. 106:341-344.-   Maxwell B. D., Roush M. L. and Radosevich S. R. 1990. Predicting the    evolution and dynamics of herbicide resistance in weed populations.    Weed Technol. 4, 2-13.-   Pimentel, D., McNair, S., Janecka, J., Wightman, J., Simmonds, C.,    O'Connell, C., Wong, E., Russel, L., Zern, J., Aquino, T. and    Tsomondo, T. 2001. Economic and environmental threats of alien    plant, animal, and microbe invasions. Agriculture, Ecosystems and    Environment 84: 1-20-   Pimentel, D., Zuniga, R., and Morrison, D. 2005. Update on the    environmental and economic costs associated with alien-invasive    species in the United States. Ecological Economics. 52: 273-288.-   Yamada, T., R. J. Kremer, P. R. de Camargo e Castro, and B. W.    Wood. 2009. Glyphosate Interactions with physiology, nutrition, and    diseases of plants: Threat to agricultural sustainability? Europ. J.    Agron. 31:111-113.

The invention claimed is:
 1. A method for selectively controlling thegrowth of at least one invasive plant species existing in a perennialgrass community, comprising: applying boron to an area of the perennialgrass community to achieve a soluble boron concentration in the soil ofthe perennial grass community from about 3 milligrams per liter to about50 milligrams per liter, and wherein said boron application isphytotoxic to the at least one invasive plant species while increasingthe growth and vigor of the perennial grass, wherein said at least oneinvasive plant species is selected from the group consisting ofcheatgrass, dandelion, and spotted knapweed.
 2. The method of claim 1,wherein said invasive plant species is cheatgrass.
 3. The method ofclaim 1, wherein said boron application produces a soil soluble boronconcentration of about 5.0 milligrams per liter to about 15.0 milligramsper liter.
 4. The method of claim 1, wherein the applied boron is aboron-containing compound.
 5. The method of claim 1, wherein saidapplied boron is a dry product.
 6. The method of claim 1, wherein thearea of the perennial grass community is a rangeland or disturbed land.7. The method of claim 1, wherein the boron is applied prior togermination or to young germinating plants of the invasive plantspecies.
 8. A method of selectively controlling the growth of at leastone invasive plant species at a locus to be treated, comprising thesteps of: a) determining the at least one invasive plant species to becontrolled in a perennial grass community; b) measuring the solubleboron concentration in soil of the perennial grass community; c)applying boron to an area of the perennial grass community to achieve asoluble boron concentration in the soil of the perennial grass communityfrom about 3 milligrams per liter to about 50 milligrams per liter,wherein said boron application is phytotoxic to the at least oneinvasive plant species while increasing the growth and vigor of theperennial grass.
 9. The method of claim 8, wherein said at least oneinvasive plant species is selected from the group consisting ofcheatgrass, dandelion, and spotted knapweed.
 10. The method of claim 8,wherein said invasive plant species is cheatgrass.
 11. The method ofclaim 8, wherein said boron application produces a soil soluble boronconcentration of about 5.0 milligrams per liter to about 15.0 milligramsper liter.
 12. The method of claim 8, wherein the applied boron is aboron-containing compound.
 13. The method of claim 8, wherein saidapplied boron is a dry product.
 14. The method of claim 8, wherein thearea of the perennial grass community is a rangeland or a disturbedland.
 15. The method of claim 8, wherein the boron is applied prior togermination or to young germinating plants of the invasive plantspecies.
 16. The method of claim 8, wherein the uppermost about 1 inchof soil achieves a soluble boron concentration of about 3 milligrams perliter to about 50 milligrams per liter.
 17. A method for negativelyimpacting the growth of at least one invasive plant species, includingthe selective control of the invasive plant species, existing in aperennial grass community rangeland, while preserving the perennialgrass community species, comprising: applying boron to an area of theperennial grass community to achieve a soluble boron concentration inthe soil of the perennial grass community from about 3 milligrams perliter to about 50 milligrams per liter in the uppermost about 1 inch ofsoil, and wherein said boron application is phytotoxic to the at leastone invasive plant species while increasing the growth and vigor of theperennial grass, wherein the at least one invasive species is selectedfrom the group consisting of cheatgrass, dandelion, and spottedknapweed, wherein said perennial grass community comprises bluebunchwheatgrass or kentucky bluegrass.
 18. The method of claim 17, whereinsaid invasive plant species is cheatgrass.
 19. The method of claim 17,wherein said invasive plant species is cheatgrass and the perennialgrass community comprises bluebunch wheatgrass.
 20. The method of claim17, wherein said invasive plant species is dandelion and the perennialgrass community comprises kentucky bluegrass.